Historians have judged the destruction of cargo vessels and oil tankers to have been the most important result of the raid, as these losses contributed to closing a supply route which was vital to the Japanese war effort.

Control of the sea was vital to the Japanese economy and war effort, as it was the conduit through which essential supplies of oil and other natural resources passed from occupied Malaya, Borneo and the Dutch East Indies.

After a short military confrontation in September 1940 the colonial government, which was loyal to the Vichy French collaborationist regime, permitted the Japanese to use ports and airfields in northern Indochina.

[10][11] While losses of oil tankers and freighters were increasingly heavy, the Japanese Government continued to order ships to make the voyage through the South China Sea.

This operation was conducted to secure airfields that could be used to attack Japanese shipping in the South China Sea and support the largest element of the liberation of the Philippines, a landing at Lingayen Gulf in north-western Luzon that was scheduled for 9 January 1945.

[13] During late 1944 Admiral William Halsey Jr., the commander of the United States Third Fleet, sought to conduct a raid into the South China Sea and led the development of plans for such an operation.

[14] In December 1944 the United States Navy's high command became concerned that the IJN would attempt to cut the supply line to the planned beachhead at Lingayen Gulf.

One of the Japanese destroyers involved in this operation was sunk, and all of the remaining ships were damaged by Allied air and naval attacks before returning to Cam Ranh Bay.

[16] As further Japanese raids were expected, senior US Navy officers believed that it was necessary to destroy the IJN's remaining mobile forces, which were thought to be split between Cam Ranh Bay and the Inland Sea in Japan.

[18] Halsey and Nimitz discussed the proposed South China Sea raid during a meeting held around Christmas 1944 at the US Navy anchorage which had been established at Ulithi atoll in the Caroline Islands.

[13] While the Fourteenth Air Force was directed to attack Japanese shipping and airfields at Hong Kong in support of the invasion of Luzon, it was not informed of the plans for the Third Fleet to enter the South China Sea.

As of 1 January 1945, both the Ise-class battleships and the small number of other Japanese warships in the region were stationed at or near Singapore, and only escort vessels operated from Cam Ranh Bay.

[2] At this time the Imperial General Headquarters was considering a major offensive against the supply line to Lingayen Gulf, but on 20 January 1945 it decided to concentrate Japan's defensive efforts on the area around the home islands and only conduct delaying actions elsewhere.

The Japanese believed that US forces could potentially land in Indochina once the liberation of the Philippines was complete, and were also concerned about possible attacks on the area by the British-led South East Asia Command.

On 3 and 4 January its aircraft carriers struck Japanese airfields on Formosa, Okinawa and nearby islands in an attempt to prevent them from being used to attack the Allied forces at Lingayen Gulf.

At around this time Vice-Admiral Thomas C. Kinkaid, the commander of the Seventh Fleet which was responsible for the Lingayen Gulf landings, asked Halsey to operate west of Luzon to provide air cover during the initial period of the invasion.

Halsey believed it would be inappropriate for his force to operate in such a passive role, and instead ordered further strikes on the Japanese airfields in southern Formosa which posed the greatest threat to Kinkaid's command.

[38] During the morning of 9 January, Nimitz released the Third Fleet from directly covering the Lingayen Gulf area, and authorized it to enter the South China Sea.

A convoy comprising seven vessels was also attacked near Cape St. Jacques in southern Indochina, leading to two freighters, three tankers, three destroyer escorts and a landing craft being sunk or forced to beach.

[48] Other Third Fleet aircraft were used to maintain a combat air patrol over the area between Tourane in central Indochina and Saigon and attack airfields, docks and oil storage facilities.

[51] The French colonial government refused to hand over the downed American airmen its forces captured to the Japanese military, and provided them with escorts to the Chinese border.

[62][63][66] The TBF Avenger torpedo bombers dispatched against Hong Kong suffered particularly heavy losses as their low-level attack runs were vulnerable to anti-aircraft fire.

Fort Dona Maria II was also attacked, possibly to destroy a radio station located within or near it, and some damage was inflicted on civilian areas and the city's harbor.

[62] As his meteorologists expected bad weather to continue into 19 January, Halsey decided to depart the South China Sea via the Surigao Strait in the central Philippines rather than sail north around Luzon.

Nimitz's reasoning was that if the fleet sailed through the central Philippines its departure would be reported by Japanese forces on bypassed islands, possibly leading to the IJN attempting a raid against the Allied supply lines.

His fleet completed fuelling on 19 January, and proceeded north towards the Balintang Channel; Task Group 30.8 separated from the main body, however, and subsequently passed through the Surigao Strait.

The commander of the Imperial Japanese Army forces in Indochina, Lieutenant General Yuitsu Tsuchihashi, believed that the raid was the precursor an Allied invasion of the area.

[69] An official court of inquiry was held,[39][87] and in 1950 the United States provided Portugal with a $20.3 million compensation payment for the damage caused to Macau's harbor on 16 January and other accidental raids on 11 and 25 June 1945.

[88] Allied air and naval attacks against Japanese shipping in the South China Sea were expanded during early 1945 as additional USAAF units moved into bases in the Philippines.

While Allied submarines and these aircraft failed to prevent the escape of the Ise-class battleships when they sailed from Singapore to Japan during Operation Kita in mid-February, the medium bombers were sinking large numbers of Japanese merchant ships by the end of the month.